The magic number

By Meredith F. Small

IT’S one of the great Christmas traditions. If you celebrate the holiday at all, by now you will probably have dispatched greetings to family, friends and colleagues. That group is unique to you, but in one remarkable respect our Christmas card lists are very similar&colon; their length. It turns out that most of us send cards to around 150 people. What’s more, this magic number of intimacy seems to be an evolutionary legacy reflecting the natural size of our species’ social groups. Even in an era of sophisticated global communication, it seems, we are only able to keep up with the same number of people as our hunter-gatherer ancestors.

It’s not easy to probe people’s card-sending habits. The holiday season is busy and stressful enough without having to answer detailed questions about each person on your list. But when UK-based anthropologists Russell Hill from the University of Durham and Robin Dunbar from the University of Liverpool roped in their own friends, they

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